1. Field of the Invention
This invention relates to an electrophotographic image forming member to be used for forming an image utilizing electromagnetic waves such as light (in the broad sense of the term, this includes ultra-violet rays, visible rays, infrared rays, X-rays, .gamma.-rays, and so forth).
2. Description of Prior Arts
For the photoconductive material constituting the photoconductive layer of the electrophotographic image forming member, there have so far been used generally various inorganic photoconductive materials such as Se, CdS, ZnO, etc., and various organic photoconductive materials such as poly-N-vinyl carbazol (PVK), trinitrofluorenon (TNF), etc.
With the electrophotographic image forming material using these photoconductive materials, however, there still remain many points to be solved. The present situation is such that various suitable electrophotographic image forming members are prepared and used by relaxing conditions for manufacture and use to a certain extent in accordance with individual circumstances. For instance, the electrophotographic image forming member using selenium (Se) alone as the photoconductive layer forming material has a narrow spectroscopic sensitivity range, and, in order to broaden it, addition of tellurium (Te) and arsenic (As) has been contemplated and practiced. However, while the electrophotographic image forming member having such Se-type photoconductive layer containing therein Te and As can really improve its spectroscopic sensitivity range, it still possesses various disadvantages such that, due to its increasing light fatigue, when one and the same image original is repeatedly and continuously used for reproduction, there take place lowering in density of the reproduced image and stain of the background (fogging in the white ground). Also, when other image originals are subsequently used for the reproduction, residual image of the preceding image original is reproduced (ghost phenomenon). Moreover, when it is exposed to the corona discharge continuously and for multiple numbers of times, the surface of the Se-type photoconductive layer undergoes crystallization or oxidation in the vicinity of the layer surface with the consequence that deterioration in the electrical characteristics of the photoconductive layer occurs.
On the other hand, the electrophotographic image forming member using ZnO, CdS, etc. as the photoconductive layer forming material involves a number of parameters determining the electrical and photoconductive characteristics as well as the physico-chemical characteristics of the photoconductive layer. It is basically a two-component type consisting of a photoconductive material and a resin binder, wherein the particles thereof are uniformly dispersed in the resin binder to form the layer. Accordingly, it has such disadvantage that, unless these various parameters are adjusted strictly and precisely, the photoconductive layer having the desired characteristics cannot be formed with satisfactory reproducibility This in turn, invites a decrease in the yield rate and mitigates against mass-production.
Further, the binder type photoconductive layer is porous in its structure due to peculiarity of the photoconductive material being dispersed in the binder. On account of this, the photoconductive layer is remarkably moisture-dependent. This is liable to bring about deterioration in the electrical characteristic when it is used in a highly humid atmosphere, and, in significant cases, a reproduced image of high quality cannot be obtained.
Furthermore, the porosity of the photoconductive layer permits intrusion of a developer into the layer at the time of the developing operation to not only promote toner image separation and reduced toner cleaning, but also cause the layer to be impossible for further use. In particular, when a liquid developer is used, the developer readily penetrates into the photoconductive layer together with its carrier solvent under acceleration by the capillary action, so that the abovementioned problems become considerable.
The electrophotographic image forming member using the organic photoconductive materials such as PVK and TNF, which have recently drawn attention of all concerned, is inferior in its moisture-resistant property, corona-ion-resistant property, and cleaning property, is poor in its photosensitivity, is narrow in its spectroscopic sensitivity range in the visible light, is deviated to the side of the short wavelengths region, and subject to various other defects, so that it is useful only to a very limited extent. Moreover, some of these organic photoconductive materials are suspected to be carcinogenic, hence there is no assurance that most of them are totally harmless to the human body.
Apart from the electrophotographic image forming members as mentioned in the foregoing, there has recently been proposed a new type of electrophotographic image forming member constituted with a photoconductive layer made of hydrogenated amorphous silicon (hereinafter abbreviated as "a-Si:H") as disclosed in, for example, DOLS 2746967 and DOLS 2855718.
The electrophotographic image forming member having the photoconductive layer constructed with such a-Si:H has a number of excellent properties in comparison with the aforementioned electrophotographic image forming members. That is, the photoconductive layer of either polarity of p-type or n-type can be fabricated depending on the manufacturing conditions; the image forming member is non-polluting; it is excellent in its wear-resistant property due to its high surface hardness; it is also excellent in its developer-resistant property; and it is further excellent in its other electrophotographic properties such as cleaning property, moisture-resistant property, and so on.
Even with the a-Si:H type electrophotographic image forming member having excellent electrophotographic characteristics in various points as mentioned above, there still exists room for improvement in respect of its light sensitivity in a practical light quantity region, its .gamma. value, its dark resistivity, its heat-resistant property in a much higher temperature region than the temperature region of ordinary use at the time of conducting a process for improving its characteristics or adding other functions thereto, and its light response property, etc.